In article <471h73$gb3 at ralph.vnet.net>, f91el at efd.lth.se (Erik Lindahl) wrote:
> Hi,
> I need to do a nonlinear fitting of data to a function, where I can't get
> an explicit expression for the functions value.
stuff deleted...
> Is there any procedure capable of this?
> I must be able to enter an equation as the model, and state that "Y" is the
> data value at each point.
> Ideas, anybody?
Just my 0.02$. A straighforward (but surely not very efficient) way is to
define an errorfunction, e.g. the sum of the squared differences of left
side and right side, and then use FindMinimum, minimizing for all the
parameters in your expressions (a, b, etc.), giving an explicit starting
point.
FindMinimum will find the minimum in the local basin of attraction where
you started your search. It is slow, but quite reliable.
Hope that helps, Christian.
Christian Jost, Universit=E9 Paris-Sud XI, Orsay, France
jost at psisun.u-psud.fr